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We report full quantum scattering calculations for near-threshold collision cross sections for excitation of Na by H. The calculations include contributions from transitions between all singlet states up to and including the ionic state (ion-pair production). The dynamics calculations are based on three sets of recent ab initio and pseudo-potential quantum-chemical calculations. Considerable sensitivity to the couplings employed is found.

We explicitly construct a (unique) Spin(9) x SU(2) singlet state, phi, involving only the fermionic degrees of freedom of the supersymmetric matrix-model corresponding to reduced 10-dimensional super-Yang Mills theory, respectively supermembranes in 11-dimensional Minkowski space. Any non-singular wave-function annihilated by the 16 supercharges of SU(2) matrix theory must, at the origin (where it is assumed to be non-vanishing) reduce to phi., QC20100629

Electronic transitions from laser excitation have produced charge transfer (CT) reactions in doped xenon solids, which in turn generate spatially separated, long-lived, dipolaron states. These quasi-stable separated charges have been as an energy storage mechanism in the study of high-energy density materials. In a previous study, we performed calculations on selected singlet electronic state of HC1, and in this study we investigate the character of the low-lying singlet electronic states in the systems Cl + Xe and HC1 + Xe. The results show at least one excited electronic state which is ionic in nature and could serve as a CT state. It is also known from experimentation that following excitation into the CT state, the H-Cl bond is ruptured. The CT state located in this study is described primarily by a molecular orbital with sigma-antibonding character in the H-Cl bonding region. This CT state would therefore provide both a charge transfer mechanism and a means for weakening or breaking the H-Cl bond consistent with experimental observations. In this report, we also provide potential energy surfaces and electronic transition probabilities as a function of R(HC1...Xe) for a linear arrangement. Electronic states, Charge transfer, High-energy density materials, Rare gas (Rg)/halides, Quantum chemistry.

Oxo complexes play a central role in the biological and inorganic chemistry of molybdenum. In the +5 oxidation state molybdenum oxo chemistry is dominated by the (Mo(V)2O3)(4+) unit, which contains a linear oxo bridge which spin pairs two d(1) centers while two terminal oxo ligands adopt syn or anti orientations perpendicular to the oxo bridge.

The photophysics of polyimides and several N-arylphthalimide model compounds has been investigated as part of an effort to understand the factors that control the oxidative photodegradation of these materials. Substituents that increase the donor-acceptor (D-A) character of both polymers and models cause an enhancement of the red-shifted electronic absorption and a shift to lower energy of the broad, weak fluorescence of these materials. Increasing solvent polarity causes a similar effect on the absorption and fluorescence spectra of the model compounds. Fluorescence quantum yields decrease with increasing D-A character in the series of model compounds, and with increasing solvent polarity for a given compound. The triplet states of both polymers and models have been characterized in solution by laser flash photolysis, and intersystem crossing quantum yields have been determined. The triplet yields also decrease with increasing D-A character of the chromophore and with increasing solvent polarity. A comparison of fluorescence and phosphorescence spectra reveals a very small singlet-triplet energy gap. It seems likely that the lowering, by increased D-A character, of the yields of the triplet states that are intermediates in the photooxidative degradation, enhances the photostability of aromatic based polymides.

The photochemical reactions of poly(methylphenyl-phosphazene) (PMPP), a disubstituted poly(phosphazene), have been studied. UV-Irradiation results in chain scission in air-saturated dichloromethane solution, whereas in the absence of molecular oxygen, a bimolecular process, leading to extensive crosslinking and gel formation, predominates. The degradation of PMPP is not inhibited by quenchers of the triplet state. The reactions of PMPP most likely originate from the singlet state. Biphenyl has been identified as a major photoproduct from PMPP both in the presence and absence of molecular oxygen.

The singlet state contribution of alpha cleavage in the photochemistry of dibenzyl ketone (DBK) and o-tolylmethylbenzyl ketone (TBK) was investigated. The fitting of a master Stern-Volmer equation for the simultaneous quenching of the S1 and T1 states of DBK and TBK leads to the conclusion that in both ketones alpha cleavage occurs in the singlet state, but to a lesser (20- 30%) extent than in the triplet. Comparison of the relative fluorescence and alpha cleavage quantum yields of DBK and TBK is also consistent with the presence of singlet state alpha cleavage in both ketones.... Photochemistry, singlet state

The photochemical and photophysical behavior of a number of methoxy-substituted benzyl alcohols has been studied in aqueous solution as a function of pH. Evidence is presented which indicates that, on excitation to the singlet excited state, the ortho and meta methoxy-substituted benzyl alcohols undergo proton-assisted loss of hydroxide ion to give the corresponding benzyl cations. These results are discussed with reference to the photoselectivity observed by Zimmerman and Sandel in the photosolvolysis of methoxybenzyl acetates.

A table of standard enthalpies of formation of all known binary compounds of sulfur and nitrogen has been compiled from a large number of MNDO type molecular orbital calculations. (Author)

Quenching of the triplet state of benzil by rare earth-tris dipivaloylmethane chelates was studied in degassed cyclohexane solutions at 18 C. A spectrophotofluorometer was used for all measurements of phosphorescence intensity. Compounds were chosen such that quenching by electronic energy transfer was not expected. Stern-Volmer graphs were constructed for the observed quenching, and the slopes from these graphs were used to calculate quenching rate constants of the order 10,000,000/M sec. The magnitude of these constants indicates that the quenching is not diffusionally controlled, and that the quenching is the result of enhanced spin-orbit coupling in the presence of the chelate. (Author)

The reaction of oxygen atoms with C3F6 has been examined further, in both the presence and the absence of molecular oxygen, at room temperature and at 126 C. The oxygen atoms were generated from the mercury-sensitized decomposition of N2O. Both (C3F6) and (O2) were varied by a factor of 10 and the lamp intensity by a factor of 200. In addition to N2, the products were CF2O, CF3CFO, C5F10 and, in the presence of O2, C3F6O (perfluoropropylene oxide). The reaction scheme is analogous to that for C2F4 and is discussed in detail. A number of relative rate constants could be estimated, and they are tabulated. Important intermediates are CF2, CF3CF, and C3F6O in the absence of O2, together with CF2O2 and CF3CFO2 in the presence of O2. (Author)

The mercury-photosensitized oxidation of C2F4 was studied at 29 and 127 C. The absorbed intensity was varied by a factor of 1000, and the O2 and C2F4 pressures by a factor of 30. The products of the reaction were cyclo-C3F6, CF2O, and C2F4O (tetrafluoroethylene oxide). Important intermediates in the oxidation are an electronically excited C2F4 molecule and the CF2O2 radical. In addition, both singlet and triplet CF2 radicals are involved. A detailed reaction mechanism is presented and several rate constant ratios are obtained. Where comparisons with literature values could be made, agreement is good.

Iminium cations can be generated by ionization of oxime polyphosphates of rigid ketones incapable of rearrangement and fragmentation. This report summarizes a research effort to determine whether singlet or triplet ions are involved as intermediates in appropriate compounds when they react to produce C-H insertion and non-stereospecific rearrangement products. Another goal of this research was to find substrates where remote intramolecular nucleophilic attack at nitrogen would supersede the conventional Beckmann isomerization. (Author)

Mossbauer absorption spectra in GeFe2O4 were measured, covering a temperature range from 77 K to 1020 K. From a first order perturbation calculation, the orbital eigenfunctions, as well as the quadrupole splitting as a function of temperature, were determined with the trigonal field splitting as a parameter. By fitting the theoretical expression for the temperature dependence of the quadrupole splitting to the experimental results was found to be (1650 plus or minus 50) K.

The reaction of O(3P) with C2F4 proceeds by the reaction scheme: O + C2F4 yields CF2O + CF2; O + C2F4 yields C2F4O; 2CF2 yields C2F4; CF2 + C2F4 yields cyclo-C3F6; C2F4O + C2F4 yields CF2O + C-C3F6; C2F4O yields CF2O + CF2 where C2F4O is excited intermediate. The ratio k5/(k11 + k5) is 0.15 at 22 C and drops slightly as the temperature is raised. The CF2 radicals produced give the same values for k3/k2(1/2) as do singlet CF2 radicals produced in another system. (Author)

Results are presented which reconcile a recently-discovered anomaly between gas-phase and liquid-phase behavior of diazomethane-methylene radical systems, and which contrast the behavior of ketene and diazomethane systems. (Author)

The objective of this work is to initiate a study on the biochemistry of ascorbic acid. Two major areas have been covered. (a) What are the sequence of events and chemical nature of the oxidation of ascorbic acid (AsH2) to monodehydroascorbic acid (AsH) to dehydroascorbic acid (dAs). (b) What are the metabolically active forms of vitamin C and their role on an enzymic level. Our progress in this work is detailed in three sections of this report: (1) Study of Ascorbate Oxidation. (2) Synthesis of Tritium Labeled Ascorbates. (3) The Ascorbate Enzyme System. In addition, cooperative work on ascorbate assays has been done in connection with the Chemical Division of the Medical Research and Nutrition Laboratories of the Fitzsimons Army Hospital, Denver. (Author), Prepared in cooperation with Fitzsimons Medical Nutritional Lab., Denver, Colo.